Diabetic retinal microvascular disease is a leading cause of blindness, although the cellular mechanisms responsible are unclear. A number of cellular defects in fuel metabolism and insulin action are known to exist in tissues such as liver, skeletal muscle, and fat in diabetes, however. The involvement of any of these defects in the pathogenesis of diabetic retinopathy has not been thoroughly investigated. In diabetes, insulin-stimulated glucose oxidation is decreased concomitantly with increased fat oxidation. Since retinal microvessels are composed of insulin- sensitive cells capable of oxidizing fatty acids, they may preferentially oxidize fat for fuel in diabetes. In this fat oxidation becomes excessive, ketone bodies may be produced. Furthermore, decreased glucose oxidation capacity could result in increased lactate production from glucose which is taken up by the cell but not oxidized. Production of ketone bodies and lactate could exceed the buffering capacity of the cells and decrease intracellular pH, or the pH in the environment surrounding the cells. Since intracellular processes are exquisitely sensitive to pH, such changes could compromise the function of the microvasculature or the surrounding retina. The specific aims of the proposed studies are therefore 1) to determine the effects of insulin on fuel selection by bovine retinal microvessels; 2) to determine the dose-response relationship between fatty acid concentration and fat oxidation and ketone body production in bovine retinal microvessels; and 3) to determine whether fat oxidation inhibits glucose oxidation in bovine retinal microvessels and whether this results in increased lactate production. The long term goal of these studies is to develop a model for studying insulin action and fuel metabolism in retinal microvessels that can be used to address the question of fuel selection and metabolic acidosis in this tissue in diabetic animals and even human diabetes.